Quantification of refractory organic material in Amazon mudbanks of the French Guiana Coast

Mid‐Holocene Grounding Line Retreat and Readvance at Whillans Ice Stream, West Antarctica

“…Though not useful for chronological purposes, higher temperature RPO intervals (RPO 2–5) were characterized by higher activation energies. Generally, these fractions contain less radiocarbon (i.e., are older) than other fractions (Rosenheim & Galy, 2012; Rosenheim, Roe, et al, 2013; Rosenheim, Santoro, et al, 2013; Williams et al, 2015), unless the low‐energy radiocarbon from was from a frozen labile source like permafrost (Schreiner et al, 2014; Zhang et al, 2017) or volatile petroleum carbon (Pendergraft & Rosenheim, 2014). Combined with stable isotopic data, mid‐ and high‐ E data can be useful in Antarctic sediments for identifying sources and amounts of relict organic carbon in a grounding‐line‐proximal environment.…”

Effect of emersion/immersion cycles on the elemental and isotopic compositions of the organic matter from surface sediments of an intertidal mud bank (French Guiana): a preliminary study

“…In French Guiana, intertidal mud banks with pioneer to young mangrove forest were characterized by potential redox values (Eh) varying from 50 to 200 mV, indicating sub‐oxic conditions in these sediments . Such conditions could also occur in our studied surface sediments because: (1) of the lack of bioturbators such as mud crabs, and of mature Avicennia germinans specimens with well developed roots and pneumatophores, both allowing oxygen exchanges between atmosphere and sediments; and (2) of a relatively low oxygen consumption (low aerobic OM degradation), resulting from the occurrence of a large fraction of mostly resistant and refractory sedimentary OM . Furthermore, the presence of MPB biofilms at the sediment surface was also responsible for pronounced gradients of oxygen, ranging from saturation below the sediment‐water interface to a complete anoxia in less than a millimeter .…”

“…[25,31] Such conditions could also occur in our studied surface sediments because: (1) of the lack of bioturbators such as mud crabs, and of mature Avicennia germinans specimens with well developed roots and pneumatophores, both allowing oxygen exchanges between atmosphere and sediments; and (2) of a relatively low oxygen consumption (low aerobic OM degradation), resulting from the occurrence of a large fraction of mostly resistant and refractory sedimentary OM. [3,25,34,35] Furthermore, the presence of MPB biofilms at the sediment surface was also responsible for pronounced gradients of oxygen, ranging from saturation below the sediment-water interface to a complete anoxia in less than a millimeter. [36] Thus, due to hypothetical low O 2 concentrations under the MPB biofilm layer in the studied stations, the microbial OM degradation processes during emersion/immersion cycles are probably denitrification.…”

“…The main potential sources of organic matter (OM) to the mud bank sediments include mangrove plants, marine and freshwater phytoplankton and also protozoa and bacteria . However, Williams et al . showed that the OM occurring in sediments from subtidal mud banks along French Guiana coast was mainly formed by refractory terrestrial material (77 %).…”

Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

“…Williams et al (2015) analyzed the 14 C distribution of POC stored mudbank sediments from the French Guiana region of the Amazon River Basin shelf by ramped pyrolysis and found that petrogenic organic carbon was absent in these sediments, suggesting that this pool of old terrestrial organic matter turns over between the floodplain and the coastal ocean. Ward et al (2013) also suggested that even lignins, considered the most recalcitrant terrestrial biomolecules (Gough et al, 1993), are actively remineralized during river transport across the basin.…”